(1) Field of the Invention
This invention relates to an interface for coupling a host terminal to a plurality of secondary terminals via standard communication chips.
(2) Background Information
FIG. 1 shows a prior art system which includes a host terminal or primary which is coupled to a plurality of secondary (Second.) terminals via a communication chip like the RS-422 XCVR. The host terminal or primary may be an NCR-5267 Financial Workstation, for example, and the secondary terminals may include a printer, magnetic card reader, keyboard, and the like. The primary polls the peripherals or secondary terminals over an RS-422 line using a conventional protocol such as Intel I8051. The NCR-5267 mentioned has a video display; however, it is not operated through the communication chip.
As an enhancement to the NCR-5267 Financial Workstation, there is provided an option which permits two bank tellers to operate their separate workstations while using the same host or primary. A teller's workstation may include several secondary terminals (shown in FIG. 1), with these secondary terminals including a printer, magnetic card reader, and a keyboard, for example.
One of the problems with the system described in the previous paragraph is that when two tellers' workstations operate from one NCR-5267 Financial Workstation, six connection nodes were required for making the connections to the tellers' workstations; three connection nodes were located in the base of the NCR-5267 and three were located in a plug-in board associated with the Workstation. One possible solution was to place a repeater in the system. However, this solution was not satisfactory because when the repeater was housed in the primary to reduce the cost of the system, the dirty signals or those containing noise from the secondary terminals were introduced into the interior of the primary. This was not a good solution because from a design standpoint, it is better to keep everything on the outside of the primary decoupled from what is on the inside of the primary to minimize noise generation and electromagnetic interference (EMI). The cables to the secondary terminals function as antennae and pick up the noise mentioned.